This invention relates to a facsimile system, particularly to a facsimile system with a function for storing image data.
Facsimile systems having an image memory for storing image data (hereinafter abbreviated as the "memory FAX") are gaining popularity in recent years. For reception, the memory FAX temporarily stores received image data and prints the stored image data at a desired timing thereafter. For transmission, on the other hand, the memory FAX reads image data to be transmitted by a scanner, temporarily stores the read image data in the image memory, and transmits the stored image data at a desired timing thereafter. Therefore, the communication time can be reduced compared with a conventional system, and the communication fees can likewise be curtailed.
However, the thus configured memory FAX has a problem due to memory capacity restrictions. That is, when a large volume of image data for memory transmission occupies the image memory, or a large volume of received image data takes up the image memory, the remaining memory capacity can no longer be sufficient to execute memory reception.
To overcome this problem, proposed in, e.g., Japanese Patent Unexamined Publication No. 91378/1989 is a system having an enciphering function. In such a system, image data stored in the image memory is enciphered when the remaining memory capacity becomes small and the enciphered image data is printed so that a free memory capacity can be reserved. An operator sets the printed document on an image reader thereafter when the free memory capacity becomes large enough so that the enciphered image data can be deciphered.
The above-mentioned conventional facsimile system, however, addresses the following problems.
(1) Since the content of enciphered image data cannot be read, the image data cannot be identified. That is, whether the image data is for transmission or reception, or to which destination the image data should be transmitted if the image data is for transmission cannot be identified. The image data is likely to be misused and thus it is difficult to manage the image data. PA0 (2) Since the content of enciphered image data cannot be read, a third part, not understanding the message that the image data is to convey, sometimes dumps the image data as an unnecessary document. PA0 (4) Since enciphered image data is printed or read out-of-position when printed on or re-read from a recorded sheet, the finally obtained image data is out of position, too. PA0 (5) Since it is only one enciphering system that is available, the enciphered image data can be deciphered easily.
(3) Since everybody can decipher image data by using a device to re-read the image data, the confidentiality is hard to be maintained.